Strippable overcoating for improved xerographic plates

ABSTRACT

A method of making a photoreceptor member which comprises: vacuum depositing a layer of photoconductive material onto a supporting substrate; forming a strippable organic overcoating over said photoconductive layer following vacuum deposition; and stripping off said overcoating whereby dust, dirt and other foreign material is trapped within the strippable coating and removed from the surface of said photoconductive layer.

United States Patent [1 1 Taylor et al.

[ STRIPPABLE OVERCOATING FOR IMPROVED XEROGRAPHIC PLATES [75] Inventors: Thomas W. Taylor, Marion;

Anthony J. Ciuffini; Paul L. Gerace, both of Rochester, all of NY.

[73] Assignee: Xerox Corporation, Stamford,

Conn.

22 Filed: Jan. 5, 1973 21 Appl. No.: 321,165

[52] 11.5. CI. 117/6, 96/1 LY, 96/1 R, 96/l.5,1l7/17.5,117/8,1l7/34,117/37 LY, 117/106 R, 252/62.1

[51] Int. Cl C03g 13/22 [58] Field of Search 117/34, 37 LY, 17.5, 6, 117/8, 106 R; 96/1 LY, l R, 1.5; 252/621 [56] References Cited UNITED STATES PATENTS 2,874,064 2/1959 Andrus 117/17.5

[ Dec. 24, 1974 Schroeder et al .1 117/34 Honjo 96/1 LY Primary Examiner-Michael Sofocleous Assistant Examiner-William R. Trenor [57] ABSTRACT 11 Claims, No Drawings BACKGROUND OF THE INVENTION This application relates to xerography, and more specifically to an improved method for fabricating photosensitive devices.

In the art of xerography, a xerographic imaging member containing a photoconductive insulating layer is imaged by first uniformly electrostatically charging its surface. The plate is then exposed to a pattern of activating electromagnetic radiation such as light, X-rays, or the like, which selectively dissipates the charge in the illuminated areas of the photoconductive insulator, while leaving behind a latent electrostatic image in the non-illuminated areas. This latent image may then be developed to form a visible image by depositing finely divided electroscopic marking particles on the surface of the photoconductive layer. This concept was originally described by Carlson in U.S. Pat. No. 2,297,691, and is further amplified and described by many related patents in the field.

Generally, the most widely used photoconductor in reusable xerography comprises a layer of vitreous selenium or selenium having a small amount of arsenic which is contained on a supporting substrate. This photoconductive layer is normally formed by vacuum evaporation techniques. U.S. Pat. No. 3,312,548 illustrates typical vacuum evaporation techniques known to the art.

In certain applications of xerography such as, for example, in xeroradiography in which X-rays are used to form a developable latent electrostatic image, a permanent organic overcoating is commonly used over the photoconductor layerJTh'e main purpose of this overcoating is to protect the plate, which is reused a number of times, against abrasion and other undesirable environmental conditions.

Normally, in the practice of vacuum evaporating photoconductive layers onto a supporting substrate, vapors of the evaporant rise upwards from an evaporation boat or other source, and condense on a supporting substrate such as a metal plate or drum which is usually supported above the source of evaporant. During this operation, undesirable effects such as the spit and spatter of dust, dirt, or the evaporant itself, end up on the surface of the photoreceptor as defects. In addition, upon allowing air to enter the vacuum chamber of coater after evaporation, the resulting turbulance causes coater dust to be thrown against the coated plate or drum, and these dust particles in many instances adhere to the photoconductor surface. This adherence of coater dust is possible because the photoconductor is still in a soft or tacky state. These defects print out in the form of either powder deficient or powder efficient spots, depending upon the type of defect, and therefore detract from the final image quality, and are a cause ofa high percentage of rejection in production quality xerographic photoreceptor plates and drums.

It is therefore an object of this invention to provide an improved method of making a photosensitive member having a reduced number of surface defects.

It is another object of this invention to provide a method of removing surface and interfacial defects on photoreceptor members.

SUMMARY OF THE INVENTION The above objects and others are accomplished in accordance with the present invention by providing a method of eliminating or reducing surface defects on photoreceptor members. One embodiment of the present invention comprises coating a photoreceptor member, which contains a photoconductive insulating layer,

in an organic solution toform a thin strippable protective organic coating or film over the photoconductive layer. This layer is then stripped off just prior to use, or prior to forming a permanent overcoating, when such overcoating is necessary on the photoconductor. As the strippable organic layer forms and dries, each dust particle or photoreceptor defect on the surface of the photoconductor trapped in the strippable coating is removed. The net result is a photoconductive surface relatively free of surface defects.

DETAILED DESCRIPTION OF THE INVENTION Any suitable strippable coating material may be used in the method of the present invention. Typical materials include organic polymers, copolymers and polymer blends. A preferred grouping of coating materials include strippable thermoplastics such as copolymers of ethylene and vinyl acetate with an auxiliary polymer such as another ethylene/vinyl acetate copolymer having a molecular weight below 10,000, more fully described in U.S. Pat. No. 3,625,727,, incorporated herein by reference; petroleum wax and an ethylene/vinyl acetate copolymer containing from 16 to 22 percent vinyl acetate, more fully described in U.S. Pat. No. 3,620,796, incorporated herein by reference; and polycarbonate resins. Any suitable commercial polycarbonate resin may be used. These resins are normally derived from bisphenol A and phosgene, and have the following structure and composition:

( e s 3h 6 5 -411 In general, the polycarbonate resin. can be formed from any dihydroxy compound and any carbonate diester, or byester interchange.

In applying the strippable overcoating, a coating solution is made by dissolving the appropriate amount of organic coating material in any suitable organic solvent, coating the photoreceptor plate or drum with the solution, and allowing the strippable coating to dry. Dip coating is one convenient method of coating, but many other suitable coating methods such as spray coating or draw coating may also be used. In general, the thickness of thestrippable coating should be thick enough to allow it to be peeled off as a substantially continuous sheet and thin enough so that the photoconductor layer is not removed. Forexample, when using a polycarbonate resin, a suitable thickness for the strippable coating is about 0.001 to 0.005 inches. The strippable coating may be removed by hand or by any convenient tool which will not scratch or mar the photoconductor or substrate surface.

In a preferred embodiment, in order to obtain optimum stripping qualities, a release agent may be applied to the surface, prior to forming the strippable overcoating. One suitable release agent comprises a solution of nigrosine in iso-propyl alcohol in a concentration of about 0.5 grams of nigrosine per 250 milliliter of the alcohol.

In the present invention, the above described technique for reducing surface defects normally is used with vitreous photoconductors such as selenium or any suitable photosensitive selenium alloy. Photosensitive vitreous selenium is described more fully by Bixby in U.S. Pat. No. 2,970,906. One example of a suitable selenium alloy comprises an arsenic-selenium photoreceptor more fully described in U.S. Pat. No. 2,803,542

to Ullrich and U.S. Pat. No. 2,822,300 to Mayer et al. Another suitable photoconductor includes a vitreous arsenic-selenium photoreceptor which further includes a small additionof a halogen such as chlorine or iodine, and is more fully described by U.S. Pat. No. 3,312,548.

Generally the strippable coatings of the present invention are used with photoreceptors of the type described above in which the photoconductive layer is generally supported on an electrically conductive support member such as brass, aluminum, nickel, steel or the like. The support may be in any convenient thickness, rigid or flexible and may be in any desired form such as a sheet, web, plate, cylinder, drum or the like. It may alsocomprise other materials such as metallized paper, plastic sheets coated with a thin layer of metal such as copper iodine or aluminum, or glass coated with a thin layer of tin oxide or aluminum.

In general, the method of the present invention is adaptable to photoreceptors which are formed by vacuum deposition. Generally, the vacuum conditions vary from about 10 to Torr. Themethod of vacuum evaporation may include coevaporation when more than one component is used in forming a photoconductive alloy layer, or flash evaporation under conditions similar to coevaporation. These techniques are more fully described in U.S. Pat. No. 3,655,377 to Sechak, which is incorporated herein by reference.

Normally in vacuum evaporation, the photoconductive material is heated to a temperature between about its melting point and considerably below its boiling point, and vapors formed from the heated evaporant are evaporated upward onto a substrate which is usually supported above the evaporant. Where a cylinder or drum is used, it is generally rotated during the entire evaporation cycle.

In most of the above methods, the substrate onto which the photoconductive material is evaporated is usually maintained at a somewhat elevated temperature in the range of about 50 to 80C.

In another embodiment of the present invention, strippable coatings are employed in the process sequence in which the coating is formed over a photoconductive substrate just prior to forming the photoconductive layer by vacuum deposition. This strippable layer when used in this instance also functions to trap dust particles or other dirt which may have inadvertently formed on the photoconductor substrate and significantly reduces substrate interface defects. Photoreceptor plates and drums using the above strippable overcoating techniques, exhibit a marked reduction in both interface photoconductive surface coating defects.

It can be seen that the strippable overcoatings of the present invention may be used over a substrate just prior to the formation of the photoconductive layer, or may separately be used following deposition of the photoconductive layer, or in both instances. In another application of the present invention, the strippable coating is removed from the photoconductor layer just prior to forming a permanent overcoating over the photoconductive layer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLE 1 An oxidized aluminum substrate in the form of a flat plate 0.080 inches thick, 9.25 inches wide and 14.25 inches long is located in a vacuum chamber approximately 8 inches above a stainless steel crucible. About 45 grams of an alloy comprising 99.67 present selenium, 0.33 percent arsenic, and 10 parts per million chlorine is placed in the crucible in the form of pellets approximately 1/8 inch in diameter. The crucible is then heated to a temperature of about 280C for about 30 minutes to form a vitreous layer about 130 microns thick on the aluminum substrate. Following the end of vacuum deposition, the vacuum chamber is cooled to room temperature, the vacuum broken, and the coated plate removed from the vacuum chamber.

EXAMPLE II A coating solution is made by dissolving grams per liter of Merlon M-50, a polycarbonate resin available from Mobay Chemical Company, in methylene chloride. One half of the plate of Example I is overcoated with the polycarbonate solution and allowed to dry to a thickness of about 0.001 inches. The polycarbonate layer is then stripped from the plate in a clean room and the entire plate is then subsequently overcoated with a polymer blend comprising a polyester, polyurethane and polyvinylidene chloride using a pour coating technique to form a permanent coating about 1 micron thick. Visual inspection of the finished plate revealed that a remarked reduction of surface defects had occurred on the stripped half. Powder cloud dusting confirmed this reduction of surface defects. The stripped half had 0.05 surface defects per square inch while the unstripped half had 1.] surface defects per square inch.

EXAMPLE III Two additional plates having the structure of the plate of Example I are dip coated in the polycarbonate solution of Example ll prior to forming the photoconductive layer. The polycarbonate coating is stripped just before forming the photoconductive layer. After coating, each plate was powder cloud dusted and the number of interface defects counted and compared to the same number of similar plates which did not use the polycarbonate stripping step. It was found that a 22 percent reduction in interface defects resulted from the use of the strippable polycarbonate coating.

Although specific components and proportions have been stated in the above description of the preferred embodiment of this invention, other suitable materials and procedures such as those listed above may be used with similar results. In addition, other materials and changes may be utilized which synergise, enhance or otherwise modify the present invention.

Other modifications and ramifications of the present invention appear to those skilled in the art upon reading the disclosure. These are also intended to be within the scope of this invention.

What is claimed is:

1. A method of making a photoreceptor member which comprises:

a. vacuum depositing a layer of photoconductive material onto a supporting substrate,

b. forming a strippable organic overcoating over said photoconductive layer following vacuum deposition; and

c. stripping off said overcoating whereby dust, dirt and other foreign material is trapped within the strippable coating and removed from the surface of said photoconductive layer.

2. The method of claim 1 which further includes forming a permanent overcoating over the photoconductive layer following the removal of the strippable overcoating.

3. The method of claim 1 in which the strippable coating comprises a thermoplastic material.

4. The method of claim 3 in which the thermoplastic comprises a polycarbonate.

5. A method of making a photosensitive member which comprises:

a. vacuum depositing a layer of photoconductive material onto a supportingsubstrate, with said photoconductive material being selected from the group consisting of vitreous selenium and vitreous selenium alloys;

b. forming a strippable organic overcoating over said photoconductive layer, following said vacuum deposition; and

c. stripping off said overcoating whereby substantially all particulate foreign matter is trapped within the overcoating and removed from the surface of the photoconductive layer.

6. The method of claim 5 which further includes forming a permanent overcoating over the photoconductor following removal of the strippable overcoating.

7. The method of claim 5 in which the overcoating comprises a strippable thermoplastic material.

8. The method of claim 7 in which the thermoplastic comprises a polycarbonate.

9. A method of making a photoreceptor member which comprises:

a. forming a strippable organic overcoating over a substrate;

b. removing said strippable overcoating immediately prior to vacuum depositing a photoconductive layer on said supporting substrate whereby substantially all particulate foreign matter originally contained on the substrate surface is trapped within the overcoating and removed from the substrate surface.

10. The method of claim 9 in which a second strippable overcoating is formed after vacuum deposition of a photoconductuve layer.

11. The method of claim 10 in which the strippable overcoating is removed prior to forming a permanent overcoating over said layer. 

1. A METHOD OF MAKING A PHOTORECEPTOR MEMBER WHICH COMPRISES: A. VACUUM DEPOSITING A LAYER OF PHOTOCONDUCTIVE MATERIAL ONTO A SUPPORTING SUBSTRATE, B. FORMING A STRIPPABLE ORGANIC OVERCOATING OVER SAID PHOTOCONDUCTIVE LAYER FOLLOWING VACUUM DEPOSITION; AND C. STRIPPING OFF SAID OVERCOATING WHEREBY DUST, DIRT AND OTHER FOREIGN MATERIAL IS TRAPPED WITHIN THE STRIPPABLE COATING AND REMOVED FROM THE SURFACE OF SAID PHOTOCONDUCTIVE LAYER.
 2. The method of claim 1 which further includes forming a permanent overcoating over the photoconductive layer following the removal of the strippable overcoating.
 3. The method of claim 1 in which the strippable coating comprises a thermoplastic material.
 4. The method of claim 3 in which the thermoplastic comprises a polycarbonate.
 5. A method of making a photosensitive member which comprises: a. vacuum depositing a layer of photoconductive material onto a supporting substrate, with said photoconductive material being selected from the group consisting of vitreous selenium and vitreous selenium alloys; b. forming a strippable organic overcoating over said photoconductive layer, following said vacuum deposition; and c. stripping off said overcoating whereby substantially all particulate foreign matter is trapped within the overcoating and removed from the surface of the photoconductive layer.
 6. The method of claim 5 which further includes forming a permanent overcoating over the photoconDuctor following removal of the strippable overcoating.
 7. The method of claim 5 in which the overcoating comprises a strippable thermoplastic material.
 8. The method of claim 7 in which the thermoplastic comprises a polycarbonate.
 9. A method of making a photoreceptor member which comprises: a. forming a strippable organic overcoating over a substrate; b. removing said strippable overcoating immediately prior to vacuum depositing a photoconductive layer on said supporting substrate whereby substantially all particulate foreign matter originally contained on the substrate surface is trapped within the overcoating and removed from the substrate surface.
 10. The method of claim 9 in which a second strippable overcoating is formed after vacuum deposition of a photoconductuve layer.
 11. The method of claim 10 in which the strippable overcoating is removed prior to forming a permanent overcoating over said layer. 